Try booting in safe mode, removing the driver and cleaning with driver cleaner, reboot, then re-install the graphics driver.
Read this thread and good luck:http://forums.nvidia.com/index.php?showtopic=187401
HiYou haven't mentioned what Gigabyte hardware you are using but it would sound as if an extended clear of the CMOS would be a good idea for starters.Remove the power cable from the mains supply and then press the power switch on the case for a few seconds just to drain any residual energy in the PSU capacitors. Once done remove the motherboard battery for at least one hour before replacing it. Next plug back into the mains supply and boot. You will now need to enter the BIOS by pressing DEL and load Optimised BIOS Defaults.Make any other changes to the BIOS settings to suit your self like disabling the floppy drive, disabling the full screen logo and making the HDD the primary boot device and then press F10 to save and exit.